This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-95382 filed on Mar. 29, 2001 and Japanese Patent Application No. 2001-239086 filed on Aug. 7, 2001.
1. Field of the Invention:
The present invention relates to a fuel injection device for injecting fuel into a corresponding cylinder of an internal combustion engine.
2. Description of Related Art:
Recently, vehicle emission regulations have become increasingly stringent. In order to reduce noxious components in exhaust gases of an internal combustion engine (hereinafter, the internal combustion engine will be referred to as an engine), it is important to atomize fuel, which is injected through fuel injection holes of a fuel injection device (hereinafter, the fuel injection device will be referred to as a fuel injector) into a corresponding cylinder of the engine. One effective measure for atomizing the fuel is as follows. That is, fuel is first heated and is then injected through the injection holes of the injector, so that the fuel boils under reduced pressure upon the injection and is thus atomized. Particularly, the fuel injected during cold start-up of the engine cannot be easily atomized and tends to adhere, for example, to an inner wall of an intake pipe. Thus, it is effective to heat the fuel during the cold start-up of the engine to atomize the fuel. In a case of an injector disclosed in Japanese Unexamined Patent Publication No. 63-170555, a fuel heater is provided to a downstream-side end surface or a side surface of a component, which defines fuel injection holes.
Temperature of the fuel heater provided to the injector for heating the fuel during the cold start-up of the engine needs to be quickly raised. For this reason, a ceramic heater is widely used as the fuel heater of the injector.
Furthermore, with reference to FIG. 15, it is conceivable to form a nozzle needle (valve member) 101, which opens and closes injection holes of an injector 100, into a hollow tubular form having a closed base end to achieve a faster response in the opening and closing operation of the injection holes of the injector 100.
However, in the injector 100 shown in FIG. 15, the fuel is conducted through an inside of the hollow tubular nozzle needle 101 and is conducted to an outside of the nozzle needle 101 through a communication hole 102. Then, this fuel is injected through the injection holes. Thus, heat of a heater 103 is not easily conducted to the fuel located inside the nozzle needle 101.
Furthermore, in order to effectively conduct the heat of the heater 103 to a valve body 104, which receives the nozzle needle 101 in a reciprocable manner, it is desirable to closely fit the heater 103 to an outer wall of the valve body 104. However, if the ceramic heater or the like, which has a relatively low mechanical strength with respect to a tensile force, is used as the cylindrical heater 103, it is difficult to closely fit the cylindrical heater 103 to the valve body 104 by press fitting the cylindrical heater 103 to an outer wall of the valve body 104 because of the relatively low mechanical strength of the ceramic heater with respect to the tensile force. Thus, an annular gap 110 needs to be provided between the heater 103 and the valve body 104, so that heat of the heater 103 is not effectively conducted to the valve body 104.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a fuel injection device that effectively heats and atomizes fuel.
To achieve the objective of the present invention, there is provided a fuel injection device including a valve body, a valve member, a heating means and a heat transfer member. The valve body includes a fuel passage, a fuel injection hole located at a downstream end of the fuel passage, and a valve seat positioned upstream of the fuel injection hole in the fuel passage. The valve member is reciprocably received in the fuel passage and has an engaging portion that is configured to be seated against the valve seat. The engaging portion closes the injection hole when the engaging portion is seated against the valve seat. The engaging portion opens the injection hole when the engaging portion is disengaged from the valve seat. The heating means directly heats at least a portion of an outer peripheral wall surface of the valve body located upstream of the valve seat. The heat transfer member is located between an inner peripheral wall surface of the valve body and the valve member. The valve member may have a hollow tubular form having a closed base end, which faces the valve seat. Furthermore, the valve member may have a communication hole, which penetrates through a peripheral wall of the valve member and is located downstream of a plane, which extends through an axial center of the heating means in a direction perpendicular to an axial direction of the valve member.
To achieve the objective of the present invention, there may be alternatively provided a fuel injection device including a valve body, a valve member, a heating means and a heat conductive resilient member. The valve body includes a fuel passage, a fuel injection hole located at a downstream end of the fuel passage, and a valve seat positioned upstream of the fuel injection hole in the fuel passage. The valve member is reciprocably received in the fuel passage. The valve member closes the injection hole when the valve member is seated against the valve seat. The valve member opens the injection hole when the valve member is disengaged from the valve seat. The heating means directly heats at least a portion of an outer peripheral wall surface of the valve body located upstream of the valve seat. The heat conductive resilient member is arranged between the valve body and the heating means and is resiliently engaged with both the valve body and the heating means. The heat conductive resilient member conducts heat of the heating means to the valve body.